A generally finely crystalline or glassy igneous rock resulting from volcanic action at or near the earth's surface, either ejected explosively or extruded as lava. The term includes near-surface intrusions that form a part of the volcanic structure.
Links to volcanism, volcanic history, volcanic rocks, and general geology by state, by region, national parks and national monuments and a brief introduction to volcanism around the U.S. entitled: Windows into the past.
Selection of photographic images of the Long Valley area that illustrate the consequences of the past geologic history of the Sierra Nevada, Long Valley Caldera, the Mono-Inyo Craters volcanic chain, glaciation, and faulting.
This booklet presents a generalized summary of the nature, workings, publications, and hazards of the common types of volcanoes around the world, along with a brief introduction to the techniques of volcano monitoring and research.